The Republican / Dave RobackHampden District Attorney makes a point in makes a point in Hampden Superior Court. Bennett, who leaves office next week, said he is prepared to stay on as a special prosecutor when former Pelham police chief Edward Fleury, seen above sitting in the background, goes on trial starting Monday. Fleury is charged with involuntary manslaughter in connection with the death of 8-year-old Christopher Bizlij, the Connecticut boy who accidentally shot himself in the head with an Uzi at a gun show Fleury had organized in 2008.

SPRINGFIELD - During an announcement about the next chapter of his professional life, outgoing Hampden District Attorney William M. Bennett reflected that while much has changed in criminal justice over his 20-year tenure, there has remained one constant.

DNA evidence and the Internet explosion has changed the face of crime and punishment, but victims and their families still want one thing: swift justice.

“I remember the very first murder case I prosecuted ... I sat with the two victims’ family members, and they filled a room just like this,” Bennett said on Tuesday morning, gesturing around a packed conference room at the downtown law firm he’ll join the day after he leaves office on Jan. 5. “All they wanted was to get the guy ... That hasn’t changed.”

After weeks of speculation, the county’s outgoing top prosecutor announced he will join Doherty, Wallace, Pillsbury & Murphy, one of the city’s larger firms at Monarch Place.

Bennett, 63, said he will focus on personal injury and business litigation, despite spending the last 35 years in the gritty world of criminal law.

The Republican / Mark M. MurrayWilliam M. Bennett, right, appears at a press conference Tuesday with Paul Doherty, of Longmeadow, when it was announced that Bennett will be joining the Springfield law firm of Doherty, Wallace, Pillsbury and Murphy, P.C., next month.

Though Bennett spent 16 years as a criminal defense lawyer before being elected district attorney in 1990, he said making the leap back to that side of the courtroom would make him feel “twisted.”

He cited the long-term relationships he has built with area law enforcement officials as the force tugging him away from a career path back to the defense bar.

“I’ve created great bonds with local police chiefs and other law enforcement agencies. I do not want to break those bonds. I do not want to tear down the good work that they have done,” Bennett said.

Defense lawyer Mark G. Mastroianni will succeed Bennett as district attorney after winning the November election by a sound margin. Bennett did not seek re-election.

Bennett said he is prepared to stay on as a special prosecutor when former Pelham Police Chief Edward B. Fleury goes on trial starting Monday. Fleury is charged with involuntary manslaughter in connection with the death of 8-year-old Christopher Bizlij, the Connecticut boy who accidentally shot himself in the head with an Uzi at a gun show Fleury had organized in 2008.

Paul S. Doherty, a partner at the law firm Bennett will join, said he is excited to add the district attorney to the current roster of 26 attorneys.

“I think you can get a sense just listening to him ... why the chemistry is so good,” said Doherty, who joined his new hire at the press conference.

Bennett follows in the footsteps of his predecessor, the late Matthew J. Ryan Jr. In 1991, after leaving office after 32 years, Ryan, too, joined Doherty, Wallace.

Bennett continued Ryan’s practice as prosecutor of personally trying major murder cases, which is not the case for district attorneys in every county. Mastroianni said he, too, intends to carry the torch on that practice.

“No doubt. That was the premise of my whole campaign,” Mastroianni said. “Whether it will be similar in terms of types and numbers of cases, or whether it will expand, we’ll have to see.”